D.c. to d.c. converter

ABSTRACT

In the d.c. to d.c. converter disclosed herein, a junction field-effect transistor is employed in a self-starting resonant oscillator circuit in which a single transformer secondary winding functions as both feedback winding and output winding. The gate-source junction of the transistor provides rectification in the output circuit.

United States Patent Terry, Jr.

[.54] D.C. TO D.C. CONVERTER [72] Inventor: Reese S. Terry, In, Miami,Fla. [73] Assignee: Cordis Corporation, Miami, Fla.

[22] Filed: Dec. 9, 1971 21 Appl. No.: 206,459

[52] US. Cl. ..32l/2, 307/25l, 307/304, 33l/lll,33l/ll2 [51] Int. Cl...H02m 3/22 [58] Field of Search.....307/25l, 304; 321/2; 330/35;332/52T;33l/lll, H2, 116, I17

3 [56] References Cited UNITED STATES PATENTS 2,854,614 9/1958 Light..32l/2 2,881,380 4/1959 Kruger ..32l/2 [15] 3,681,674 [451 Aug. 1, 19723,491,281 1/1970 Penn ..33l/112X OTHER PUBLICATIONS Fet Converter lsSelf-Oscillating" Electronics, Dec. 23, 1968, PP- 62- 63 PrimaryExaminer-William M. Shoop, Jr. Attorney-Herbert W. Kenway et a].

571 a ABSTRACT 8 Claims, 1 Drawing Figure 1 me. To 0.0. CONVERTERBACKGROUND OF THE INVENTION The present invention relates to d.c. tod.c. converters and more particularly to such a converter which isefficient at low power levels and voltages.

While various d.c. powered inverters and converters have been devisedheretofore, these prior art devices have not ordinarily been suited foroperation at very low power levels, e.g., a milliwatt and below. Rather,the operation of prior art converters has typically been such thatefficiency was greater at higher power levels than at low power levels,particularly with the common square-wave or saturating type inverter.Also, a problem with many types of prior art inverter circuits was thatthey were not self-starting, that is, special circuitry had to beprovided to initiate oscillation or, in some cases, to temporarilydisconnect the load during starting.

In certain applications, however, the ability to efficiently convertd.c. power at one low voltage level to a different voltage level isdesirable, even though the power levels may be quite low. One particularexample is in the construction of implantable cardiac pacers. As isknown, both the efficiency and reliability of an electrochemical powersource are improved if the number of cells employed is reduced. In otherwords, a single cell of a given size is more efficient than a multiplecell unit of the same physical size or mass. Likewise, the single cellis much less likely to fail than the multiple cell. Heretofore, however,it has been necessary to employ a multiple-cell power pack forimplantable pacers in order to provide the voltages required by thetypical pacer circuitry. Furthermore, certain power sources now underdevelopment for use in implantable cardiac pacers are adapted to providecurrent at relatively low voltages. For example, the so-called atomicbattery typically provides a source potential of about half a volt. Incontrast, present cardiac pacer designs require supply potentials in theorder of 3 to 6 volts or even higher.

While the use of a power converter of any sort necessarily entails someloss, the availability of a reasonable conversion efficiency atextremely low power levels may make it advantageous to use a low voltagesource to power higher voltage circuits due to the increased efficiencyand reliability obtainable from the source itself since a single cellmay be used instead of a multiple cell, thereby increasing the ratio ofactive material to package weight and by decreasing the likelihood ofstatistical failure.

Among the several objects of the present invention may be noted theprovision of a d.c. to d.c. converter which provides reasonableefficiency at quite low power levels; the provision of such a converterwhich will operate with very low supply voltages; the provision of sucha converter which is self-starting; the

provision of such a converter which is highly reliable;

the provision of such a converter which requires very few components andwhich is of relatively simple and inexpensive construction. Otherobjects and features will be in part apparent and in part pointed outhereinafter.

SUMMARY OF THE INVENTION Briefly, a d.c. to d.c. converter according tothe present invention is adapted for coupling a d.c. source providingcurrent at one voltage to a load adapted to utilize direct current at adifferent voltage. The inverter employs a resonant transformer having aninput winding and an output winding, these windings being insulated fromeach other. The converter also employs a junction field-effecttransistor having a pair of terminals with a resistive channel circuittherebetween and a gate terminal, there being a rectifying semiconductorjunction between the gate terminal and the channel circuit. Theconductivity of the channel circuit is variable as a function of thevoltage appliedto the gate terminal with respect to the channel circuit.The primary winding of the transformer is connected in series with thechannel circuit across the source while one end of the secondary windingis connected to the gate terminal, substantially directly. Thewindingsare polarized so that regenerative feedback is provided.

v The other end of the secondary winding is connected to BRIEFDESCRIPTION OF THE DRAWING The single FIGURE is a schematic circuitdiagram of a d.c. to d.c. converter according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,there is indicated at 11 a resonant transformer having a primary orinput winding 13 and a secondary or output winding 15, these windingsbeing insulated from each other. Typically, the distributivecapacitances of the windings 13 and 15, shown in broken lines andindicated at 17 and 19 respectively, will be sufficient to render thetransformer ll suitably resonant for the purposes of the presentinvention. However, if needed, an additional tuning capacitance may beadded to one or to both of the windings, e.g., as indicated at 21 inparallel with the secondary winding 15.

Resonant oscillations in transformer 11, are driven by means of ajunction field-effect transistor 23. Transistor 23 includes a sourceterminal 25 and a drain terminal 27, there being a resistive channelcircuit extending therebetween. Transistor 23 also includes a gateterminal 29. As is understood with regard to this type of transistor,there is a semiconductor rectifying junction between the gate terminal29 and the resistive channel circuit. This junction is referred to asthe gatesource junction. As is likewise understood, conduction throughthe channel circuit is variable as a function of the voltage orpotential applied to the terminal 29 with respect to the terminal 25.Preferably, transistor 23 is of the depletion mode type so that someconduction will exist in the channel circuit when zero potential existsbetween the gate terminal 29 and the source terminal 25. In theembodiment illustrated, transistor 23 is of the N-channel type but itshould be understood that the opposite or P-conductivity type may beused with a corresponding reversal of polarities.

As indicated in the drawing, the primary winding 13 and the channelcircuit of transistor 23 are connected in series across a pair of d.c.input terminals 31 and 33.

Terminals 31 and 33 are adapted to receive d.c. power from a low voltagesource, e.g., the single electrochemical cell indicated at 35. In theembodiment illustrated, the lead 34 connected to terminal 33 may beconsidered to be ground potential and the source 35 provides a positivepotential with respect thereto.

One end of the secondary winding is connected essentially directly tothe gate terminal 29 while the other end of this winding is connected toan output terminal 37 which constitutes one side of the load circuit.The other side of the load circuit is constituted by a terminal 39 whichis connected to one side of the source circuit, i.e., to the terminal 33through the ground lead 34 in the embodiment illustrated. A suitableresistive load is indicated at 41 in the drawing. The output circuit isshunted by a filter capacitor 43 which, as is explained in greaterdetail hereinafter, performs the functions of converting unidirectionalcurrent pulses to direct current and of providing a d.c. referencepotential for the feedback circuit operation. While the capacitor 43 isshown in the embodiment illustrated as a component of the converteritself, it should beunderstood that the load with which the converter isto be used may possess sufficient shunt capacitance so that no separatecapacitor in the converter is needed.

As indicated by the conventional dot notation in the drawing, thepolarities of the windings of 13 and 15 are such that positive orregenerative feedback is'supplied around the transistor 23, that is, thegate terminal 29 is driven to a more positive potential as the drainterminal 27 is pulled to a more negative potential by conduction throughthe channel circuit.

Assuming that no voltage exists across the'load 41 and the filtercapacitor 43 when the source is initially connected, some nominal amountof conduction will exist in the transistor channel. Accordingly, gainwill be present so that the positive feedback provided will cause anyinitial perturbation to grow into a sustained oscillation. Asoscillation builds up, the rectifying action provided by thesemiconductor junction between the gate terminal29 and the channelcircuit will cause the oscillatory feedback signal to be rectified.Accordingly, the output terminal 37 will be driven, by this rectifiedcurrent component, to a potential which is negative with respect toground. Whenequilibrium is reached, i.e., sustained oscillation, theupper end of winding 15 will be maintained at a negative d.c. potentialsuch that only the most positivegoing excursions of the opposite end ofthe winding will forward bias the base-source junction. However, sincethese pulses of current will be in phase with the conduction through theprimary winding 13, the oscillations will be sustained. In this state,the transistor 23 may thus be considered to be in class C operation.Furthermore, since the gate-source junction provides rectification ofthe feedback signal, no separate rectifier is needed to obtain aunidirectional output current. Thus, a very simple'construction isprovided in which only a resonant transformer and a junctionfield-effect transistor are needed, together with a filter capacitor ifthe load circuit itself is not sufficiently capacitive.

In a particular embodiment of this inverter, the transformer 11comprised a Ferroxcube pot core model 1408 with a primary winding of 18turns of No. 30 wire and a secondary winding of 380 turns of Number 38wire. The transistor 23 was a type 2N4858. The transformer thusconstructed was resonant with a Q of 18 without any separate resonatingcapacitor. With an input voltage of 0.4 volts, this circuitwould'develop about 7 volts across a 180 K ohms load, thereby providinga measured efficiency of better than percent. A separate filtercapacitor was provided.

Since the converter draws a pulsating current from the source, it may insome circumstances be desirable to shunt the source with a filtercapacitor if the source exhibitsa relatively high resistance. Similarly,if improved output regulation is needed, a Zener diode may be placedacross the output circuit of the converter to lower its effective sourceimpedance.

In view of the foregoing, it may be seen that several objects of thepresent invention are achieved and other advantageous results have beenattained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it should be understood thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:

1. A d.c. to d.c. converter for coupling a d.c. source providing currentat one voltage to a load adapted to utilize unidirectional current at adifferent voltage, said converter comprising:

a resonant transformer having an input winding and an output winding,said windings being insulated from each other;

a junction field-effect transistor having a pair of terminals with asubstantially resistive channel circuit therebetween and a gateterminal, there being a rectifying semiconductor junction between saidgate terminal and said channel circuit, the conductivity of said channelcircuit being variable as a function of the voltage applied to said gateterminal with respect to said channel circuit;

5 said channel circuit for connection across said source; meanssubstantially directly connecting one end of said secondary winding tosaid gate terminal; means for connecting the other end of said secondarywinding to one side of said load circuit; and means for connecting theother side of said load circuit to one side of said source, whereby saidtransformer is driven into resonant oscillation by said transistor andrectification, by said junction, of the oscillatory signal induced insaid output winding generates a unidirectional current in said loadcircuit. 2. A converter as set forth in claim 1 including a tuningcapacitor shunting at least one of said windings.

means connecting said primary winding in series with r 6. A dc. to d.c.converter for coupling a d.c. source providing current at one voltage toa load adapted to utilize direct current at a different voltage, saidconverter comprising:

8. A d.c. to d.c. converter for coupling a d.c. source providing apositive potential with respect to ground to a load adapted to utilizedirect current at a higher voltage, said converter comprising:

a resonant transformer having an input winding and 5 a resonanttransformer having an input winding and an output winding, said windingsbeing insulated an output winding, said windings being insulated fromeach other; 7 from each other, said output winding having a subajunction field-effect transistor of the depletion stantially greaternumber of turns than said input mode type having source and drainterminals with winding;

a resistive channel circuit extending therebetween to a junctionfield-efiect transistor of the depletion and a gate terminal forcontrolling conduction mode type having source and drain terminals withthrough said channel circuit, there being a rectifyan N-type resistivechannel circuit extending ing semiconductor junction between said gatetertherebetween and a gate terminal for controlling minal and saidchannel circuit; conduction through said channel circuit, there meansfor connecting said source terminal to one being a rectifying P-Nsemiconductor junction side of said current source; between said gateterminal and said channel cirmeans for connecting one end of said inputwinding cuit;

to said drain terminal and the other end to the means for connectingsaid source terminal to ground; other side of said current source; meansfor connecting one end of said input winding a filter capacitor one endof which is connected to to said drain terminal and the other end tosaid said one side of said current source; positive source potential;

means connecting one side of said output winding to a filter capacitorone end of which is connected to the other end of said capacitor; andground;

means connecting the other side of said output windmeans connecting oneside of said output winding to ing to said gate terminal, the ends ofsaid input and the other end of said capacitor; and output windingsconnected to said transistor being means connecting the other side ofsaid output windoppositely polarized thereby to provide positive ingdirectly to said gate terminal, the ends of said feedback around saidtransistor, input and output windings connecte to said whereby saidtransformer is driven into resonant tran15tr opposlte y polanzfid telieby to oscillation by said transistor and rectification, by ProvldePosmve feedback around Said translstor,

said junction, of the oscillatory signal induced in said output windinggenerates at said other end of said filter capacitor a d.c. voltage ofpolarity opposite to that applied to said input winding by said wherebysaid transformer is driven into resonant oscillation by said transistorand rectification, by said semiconductor junction, of the oscillatorysignal induced in said output winding generates a source, with respectto the potential at said source FP Voltage of magnitude greater f SaidterminaL positive voltage at said other end of the said filter 7. Aconverter as set forth in claim 6 including a tuncapacltoring capacitorshunting one of said windings.

1. A d.c. to d.c. converter for coupling a d.c. source providing currentat one voltage to a load adapted to utilize unidirectional current at adifferent voltage, said converter comprising: a resonant transformerhaving an input winding and an output winding, said windings beinginsulated from each other; a junction field-effect transistor having apair of terminals with a substantially resistive channel circuittherebetween and a gate terminal, there being a rectifying semiconductorjunction between said gate terminal and said channel circuit, theconductivity of said channel circuit being variable as a function of thevoltage applied to said gate terminal with respect to said channelcircuit; means connecting said primary winding in series with saidchannel circuit for connection across said source; means substantiallydirectly connecting one end of said secondary winding to said gateterminal; means for connecting the other end of said secondary windingto one side of said load circuit; and means for connecting the otherside of said load circuit to one side of said source, whereby saidtransformer is driven into resonant oscillation by said transistor andrectification, by said junction, of the oscillatory signal induced insaid output winding generates a unidirectional current in said loadcircuit.
 2. A converter as set forth in claim 1 including a tuningcapacitor shunting at least one of said windings.
 3. A converter as setforth in claim 1 including a filter capacitor shunting said loadcircuit.
 4. A converter as set forth in claim 1 in which said transistoris of the depletion mode type.
 5. A converter as set forth in claim 1wherein said other side of the load circuit is connected to the side ofsaid current source which is connected to said transistor channelcircuit.
 6. A d.c. to d.c. converter for coupling a d.c. sourceproviding current at one voltage to a load adapted to utilize directcurrent at a different voltage, said converter comprising: a resonanttransformer having an input winding and an output winding, said windingsbeing insulated from each other; a junction field-effect transistor ofthe depletion mode type having source and drain terminals with aresistive channel circuit extending therebetween and a gate terminal forcontrolling conduction through said channel circuit, there being arectifying semiconductor junction between said gate terminal and saidchannel circuit; means for connecting said source terminal to one sideof said current source; means for connecting one end of said inputwinding to said drain terminal and the other end to the other side ofsaid current source; a filter capacitor one end of which is connected tosaid one side of said current source; means connecting one side of saidoutput winding to the other end of said capacitor; and means connectingthe other side of said output winding to said gate terminal, the ends ofsaid input and output windings connected to said transistor beingoppositely polarized thereby to provide positive feedback around saidtransistor, whereby said transformer is driven into resonant oscillationby said transistor and rectification, by said junction, of theoscillatory signal induced in said output winding generates at saidother end of said filter capacitor a d.c. voltage of polarity oppositeto that applied to said input winding by said source, with respect tothe potentiAl at said source terminal.
 7. A converter as set forth inclaim 6 including a tuning capacitor shunting one of said windings.
 8. Ad.c. to d.c. converter for coupling a d.c. source providing a positivepotential with respect to ground to a load adapted to utilize directcurrent at a higher voltage, said converter comprising: a resonanttransformer having an input winding and an output winding, said windingsbeing insulated from each other, said output winding having asubstantially greater number of turns than said input winding; ajunction field-effect transistor of the depletion mode type havingsource and drain terminals with an N-type resistive channel circuitextending therebetween and a gate terminal for controlling conductionthrough said channel circuit, there being a rectifying P-N semiconductorjunction between said gate terminal and said channel circuit; means forconnecting said source terminal to ground; means for connecting one endof said input winding to said drain terminal and the other end to saidpositive source potential; a filter capacitor one end of which isconnected to ground; means connecting one side of said output winding tothe other end of said capacitor; and means connecting the other side ofsaid output winding directly to said gate terminal, the ends of saidinput and output windings connected to said transistor being oppositelypolarized thereby to provide positive feedback around said transistor,whereby said transformer is driven into resonant oscillation by saidtransistor and rectification, by said semiconductor junction, of theoscillatory signal induced in said output winding generates a negativevoltage of magnitude greater than said positive voltage at said otherend of the said filter capacitor.